In a conventional lens, an incoming light ray is refracted when it enters the shaped lens surface because of the abrupt change of the refractive index from air to a homogeneous lens material. The surface shape of the lens determines the focusing and imaging properties of the lens. In a GRIN lens, there is a continuous variation of the refractive index within the lens material. In a simple GRIN lens, plane optical surfaces can be used. The light rays are continuously bent within the lens. The focusing properties are determined by the variation of refractive index within the lens material.
U.S. Pat. No. 5,262,896 describes the fabrication of axial gradient lenses by the controlled diffusion process. The blanks for the fabrication of such gradient lenses can be made by a variety of processes, such as SOL-GEL, infusion, and diffusion and may be glass, plastic or other suitable optical material.
U.S. Pat. No. 4,956,000 describes a method and apparatus for fabricating a lens having a radially non-uniform but axially symmetrical distribution of lens material, in which the lens size and shape is determined by the selective direction and condensation of vaporized lens material onto a substrate.
U.S. Pat. No. 5,236,486 describes the forming of a cylindrical or spherical gradient lens blank from an axial gradient lens blank by heat molding (slumping). This process produces a monolithic lens with a continuous index of refraction profile.
U.S. Pat. No. 7,002,754 describes a hierarchically multilayered polymer composite for graded index of refraction (GRIN) lenses and a method to fabricate the same.